The present invention generally relates to coordinate input apparatuses, and more particularly to a coordinate input apparatus which inputs coordinate information related to a position on a touch panel when pressure is applied at this position by a pen or the like.
Recently, various kinds of input apparatuses have been developed for inputting hand-written information to a computer or the like. Such input apparatuses use a coordinate input apparatus having a touch panel, and coordinate information related to a position on the touch panel is detected by the coordinate input apparatus when pressure is applied at this position by a pen or other pressure applying member. In this coordinate input apparatus, it is essential that the position on the touch panel where the pressure is applied can be detected with a high accuracy.
For example, a Japanese Laid-Open Patent Application No. 56-11582 proposes a coordinate input apparatus using switching elements which use diodes. A plurality of point electrodes are provided on a resistor layer, and the switching elements are used to control voltages which are applied in X and Y directions of the point electrodes. When a pressure is applied by a pen or the like at an arbitrary position on a conductor layer which confronts the resistor layer, this arbitrary position is recognized by detecting the position in both the X and Y directions.
On the other hand, a Japanese Laid-Open Patent Application No. 58-35679 proposes a coordinate input apparatus using analog switches as the switching elements.
In the coordinate input apparatuses proposed in the Japanese Laid-Open Patent Applications No. 56-11582 and No. 58-35679 described above, the point electrodes are connected to the resistor layer, and voltages are applied to the point electrodes via the corresponding switching elements so as to obtain a potential distribution which is uniform along the X and Y directions. However, the switching elements are provided on a substrate which is independent of a substrate which is provided with the resistor layer. For this reason, there was a problem in that a number of wiring lines corresponding to the number of point electrodes must be drawn out from the substrate which is provided with the resistor layer.
In other words, the equipotential lines of the acting electric field become approximately linear at the peripheral part of the touch panel if a large number of point electrodes are provided with respect to each side of the touch panel. The position detecting accuracy is improved by providing the large number of point electrodes. However, as the number of point electrodes increases, the number of wiring lines which must be drawn out from the point electrodes increases considerably. For example, if nine point electrodes are provided with respect to one side of the touch panel, it is necessary to provide thirty-six wiring lines which are drawn out from the nine point electrodes.
On the other hand, it must be possible to distinguish the pressure applied on the touch panel by an operator's hand and the pressure applied by the pen. But in order to realize the electrical contact between the conductor layer and the resistor layer only if the pressure is applied on the touch panel by the pen, the tip of the pen must be made extremely fine. In addition, there was a problem in that an accurate coordinate detection cannot be made unless the electrical contact between the conductor layer and the resistor layer is detected with a short detection period by turning the switching elements ON/OFF at extremely short intervals. This is because spacer pieces provided between the conductor layer and the resistor layer are extremely small and are arranged at extremely fine intervals.